South Kensington or Victoria Station?

Accomodation near South Kensington tends to be nicer than the one around Victoria Station, but you can get cheaper rooms there. No area is particularly unsafe, you need to keep your wits with you no matter where you are.Pickpockets can operate anywhere.
There is a lot of construction going on near Victoria Station, it's noisy and very dusty and I doubt this will be finished by October. I'd choose South Kensington.

Not far between to the two areas, but less construction work (so quieter and less dusty) and fewer pickpockets round South Keningston or Gloucester Road tube stations than Victoria. South Kensington is more convenient (a few minutes walk) for museums (Natural History, Science & Victoria & Albert {art}), Royal Albert Hall, Royal Geographical Society, Kensington Gardens, Hyde Park etc.

Both are safe, as long as you keep valubles in pockets close to body / zipped, don't look like a gormless lost tourist etc. Check map before you get to street, out away, walk confidently and you'll be fine.

South Kensington Tube Station is just one of London's many landmarks to discover. Visitors can find the best hotel prices near many Train, Metro and Bus Stations - A wide range of hotels are available near South Kensington Tube Station, from the friendly St. Mark Hotel to the luxurious Belgraves - A Thompson Hotel.

South Ken anytime if you can afford it.

This is Chelsea come on, King's road !!!